MCM-68 is a single crystalline phase molecular sieve material which has a unique 3-dimensional channel structure comprising one 12-membered ring channel system and two 10-membered ring channel systems, in which the channels of each system extend perpendicular to the channels of the other systems and in which the 12-ring channels are generally straight and the 10-ring channels are tortuous (sinusoidal). MCM-68 has been assigned structure type MSE by the Structure Commission of the International Zeolite Association.
The composition and characterizing X-ray diffraction pattern of MCM-68 are disclosed in U.S. Pat. No. 6,049,018, which also describes the synthesis of the molecular sieve in the presence of a structure directing agent comprising the N,N,N′,N′-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium dication. The entire contents of U.S. Pat. No. 6,049,018 are incorporated herein by reference.
U.S. Pat. No. 6,049,018 exemplifies the use of MCM-68 as a catalyst in aromatic alkylation and transalkylation reactions. In addition, U.S. Pat. No. 7,198,711 discloses that MCM-68 shows activity in the catalytic cracking of hydrocarbon feedstocks to produce an enhanced yield of butylenes and isobutene, with the MCM-68 either being the primary cracking catalyst or an additive component in conjunction with a conventional large pore cracking catalyst, such as zeolite Y.
To date, however, the commercial development of MCM-68 has been hindered by the high cost of the dication structure directing agent required for its synthesis and hence there is significant interest in finding alternative, less expensive structure directing agents for the synthesis of MCM-68.
According to the present invention, it has now been found that 1,1-dialkyl-4-cyclohexylpiperazin-1-ium cations and 1,1-dialkyl-4-alkylcyclohexylpiperazin-1-ium cations are effective as structure directing agents in the synthesis of MCM-68. Moreover, it has been found that these cations can be produced conveniently and inexpensively from commercially available raw materials.
European Patent Publication No. EP 1 852 394 A1, published Jul. 11, 2007 and incorporated herein by reference, discloses that the zeolite ITQ-32 can be synthesized in the presence of fluoride ions using 1,1-dimethyl-4-cyclohexylpiperazin-1-ium cations as a structure directing agent. ITQ-32 has a 2-dimensional channel structure comprising 8-membered ring channels and has been assigned structure type IHW by the Structure Commission of the International Zeolite Association. Thus ITQ-32 has a different crystal structure than MCM-68. Moreover, in EP 1 852 394 A1 the 1,1-dimethyl-4-cyclohexylpiperazin-1-ium are produced by alkylation of N-cyclohexylpiperazine with iodomethane, but N-cyclohexylpiperazine is not commercially available and is scarce even at laboratory scale quantities.